@namespace

Syntax

@namespace [ prefix ] URI;

Description

The
@namespace at-rule declares an XML namespace and,
optionally, a prefix with which we can refer to it.
@namespace rules must follow all
@charset and @import rules,
and precede all other at-rules and rule sets in a style sheet.

The
scope of an @namespace rule is the style sheet in
which it’s declared—it doesn’t extend to imported style sheets.

If
no prefix is specified in the @namespace rule, the
rule defines the default namespace.

If a prefix is specified, you
can refer to elements in that namespace by prepending the prefix and a
vertical bar, |, to the element selector,
like so:1